Fluid-actuated cylinder and method for manufacturing it

ABSTRACT

A fluid-actuated cylinder and a method for manufacturing it, including a head and a connecting tube to be coupled; coupling is obtained by compression of the two members along their axis, deforming the end of the tube by using, as a die for the deformation of the tube, a particular ring which is fitted on the head member and is coaxial thereto.

[0001] The present invention relates to a fluid-actuated cylinder and to a method for manufacturing it.

[0002] The mutual assembly of a head and a tube of pneumatic cylinders is a critical operation, because once the seal has been provided between the tube and head at the different operating pressures, the assembly must ensure resistance to the thrust applied by the operating pressure to the cross-section of the head, resistance to the axial mechanical stresses applied by the mass connected to the stem-piston assembly, and resistance to the torsional stresses that occur during the fixing of the cylinder.

[0003] Various methods are known which allow head-tube coupling according to the characteristics that the head-tube assembly is to have in order to withstand the operating stresses.

[0004] EP-A-0351317, U.S. Pat. No. 4,073,219, FR-A-2544806 disclose methods for assemblying cylinders.

[0005] One method in particular, and specifically the cylinder with rolled tube method, provides a product whose mechanical characteristics determine a field of use which includes the products manufactured with the method according to the present invention.

[0006] In the cylinder with rolled tube method, the head-tube coupling is provided by way of the deformation of the tube, which is obtained by rolling and subsequent upsetting the edge of the heads onto the tube. The seal is provided by means of an O-ring or by a mechanical compression seal.

[0007] In particular, this fastening method has the drawback of requiring an expensive assembly apparatus, including a customized numeric-control lathe, and suitable tools for rolling the different diameters.

[0008] Another drawback relates to the particularly long times for tooling and programming the machine for rolling the different diameters and for the rolling and upsetting operations.

[0009] Another drawback is that the method is hardly flexible and requires large investments in machines in order to meet market requirements.

[0010] The aim of the present invention is to provide a method for the assembly of fluid-actuated cylinders and the like which overcomes the drawbacks of the cited prior art.

[0011] Another object of the invention is to provide an assembled product which is reliable in use and has competitive costs.

[0012] This aim, this object and others, which will become better apparent hereinafter, are achieved by a fluid-actuated cylinder and the like comprising at least one head which is applied hermetically to the end of a tube which is folded inside an annular groove formed in the head, characterized in that it comprises a deformation ring which is arranged between the head and the folded end of the tube.

[0013] This aim, this object and others, which will become better apparent hereinafter, are also achieved by a method for manufacturing fluid-actuated cylinders comprising at least one head and a tube to be coupled, characterized in that it includes the steps of:

[0014] forming a groove in an outer cylindrical surface of the head proximate to the coupling region, applying a ring comprising a chamfered internal surface, at a tapering portion, which has a similar radiusing, formed on the outer surface of the head;

[0015] performing an axial compression between the head and the tube, sliding the end of the tube inside the groove, so that the end of the tube is deformed and compressed against the tapering portion of the head member, forcing the ring to maintain a forced arrangement between the head member and the connecting tube with elastic reaction.

[0016] Further characteristics and advantages of the present invention will become better apparent from the description of preferred but not exclusive embodiments thereof, illustrated only by way of non-limitative example in the accompanying drawings, wherein:

[0017]FIG. 1 is a partially sectional side elevation view of a head applied to a cylinder, illustrating an initial step of assembly according to the invention;

[0018]FIG. 2 is an enlarged-scale view of FIG. 1, showing in detail the surface of the tube that enters the groove;

[0019]FIG. 3 is a side elevation view, similar to FIG. 1, of an intermediate step of assembly, according to the invention;

[0020]FIG. 4 is an enlarged-scale view of FIG. 3, showing in detail the surface of the tube that is deformed;

[0021]FIG. 5 is a view, similar to FIGS. 1 and 3, of a final step of assembly according to the invention;

[0022]FIG. 6 is an enlarged-scale view of FIG. 5, showing in detail the surface of the tube, forced between the head and the ring.

[0023] With reference to the above figures, a fluid-actuated cylinder according to the invention, designated by the reference numeral 100, has a head 3, which is applied hermetically to the end of a tube 6, and a ring 1 with a particular internal radiusing which constitutes a chamfered surface 2 which has a radius of its own.

[0024] The ring 1 is fitted on a tang 13 which is monolithic with the head 3 at a tapering portion 4 which is formed on the outer surface of the tang. The particular configuration of the chamfered surface 2 of the ring 1 and of the tapering portion 4, which follows the profile of the internal chamfered surface 2, forms a groove 5 around the cylindrical surface of the tang 13. The groove is used as a die for guiding the deformation of an end 16 of the tube 6 to be coupled to the head 3, so that by being trapped between the head 3 and the ring 1 the assembly of the members is ensured.

[0025] In particular, as shown in FIGS. 1 and 2, by axial compression, represented schematically by the arrow F, between the head 3 and the tube 6, the end 16 of the tube 6 is made to slide inside the groove 5. The internal chamfer 2 of the ring 1, together with the tapering portion 4 which has a similar radius of curvature, guides the end 16 of the tube 6 in its deformation until contact occurs with the head 3 on a bottom 7 of the groove 5, as shown in FIG. 4. During deformation, the ring 1 transfers the compression force to the tube 6, but when the end 16 of the tube 6 rests against the head 3 it is the tube itself that discharges the compression force onto the ring 1, which compresses the folded part of the tube 6 against the tapering portion 4 of the head 3, as shown in FIG. 6.

[0026] Such final step ensures tightness at the operating pressures and forces the ring 1 to maintain a forced arrangement between the elastic reaction of the tube 6 against the head 3 and the head itself.

[0027] A condition is thus produced by way of which the only way to remove the head is to widen the ring or cut the tube.

[0028] Advantageously, a system for centering the ring 1 on the head 3 is provided.

[0029] The fastening method according to the invention has the advantage that it can use a simple press in order to assemble heads and tubes of various diameters by simply changing the centerings, with low costs in terms of investments in machines and with great flexibility.

[0030] The assembly of the front and rear heads occurs by means of a single operation, in shorter times, making the system more competitive from the economic point of view.

[0031] The interference produced between the tube and the head further ensures tightness without gaskets and very high resistance to axial thrusts and torsion.

[0032] In practice it has been observed that the invention achieves the intended aim and objects.

[0033] The cylinder and the method according to the invention are susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; all the details may furthermore be replaced with technically equivalent elements.

[0034] The materials used, as well as the dimensions, may of course be any according to requirements and to the state of the art. 

1. A fluid-actuated cylinder comprising at least one head which is applied hermetically to the end of a tube which is folded inside an annular groove formed in said head, characterized in that it comprises a deformation ring which is arranged between said head and said folded end of said tube.
 2. The cylinder according to claim 1, characterized in that said deformation ring is fitted on said head at a tapering portion of the surface of the head.
 3. The cylinder according to claim 1 or 2, characterized in that said deformation ring comprises a convex chamfered internal surface which has its own radius of curvature.
 4. The cylinder according to one or more of the preceding claims, characterized in that said tapering portion comprises a radius of curvature which corresponds to the radius of curvature of said internal surface of said deformation ring.
 5. A method for manufacturing a fluid-actuated cylinder comprising at least one head and a tube to be coupled, characterized in that it comprises the steps of: forming a groove in an outer cylindrical surface of said head proximate to the coupling region, applying a ring which comprises a chamfered internal surface, at a tapering portion, having a similar radiusing, which is formed on said outer surface of said head; performing an axial compression between said head and said tube, making the end of said tube slide inside said groove, so that said end of said tube is deformed and compressed against said tapering portion of said head member, forcing said ring to maintain a forced arrangement between said head member and said connecting tube by elastic reaction.
 6. A device for the hermetic assembly of at least one head and a tube which are adapted to constitute a fluid-actuated cylinder, characterized in that it comprises a deformation ring which can be applied to said head at a tapering portion of said head in order to form a groove in which the end of said tube is deformed by axial compression of said tube and said head. 